The present invention relates to electronic systems aboard aircraft. In particular, the invention relates to health monitoring of electronic systems aboard aircraft.
Aircraft require highly reliable electronic systems to ensure safe and efficient operation. Malfunctions in critical electronic systems, such as an Electronic Engine Controller (EEC) or a Full Authority Digital Engine Controller (FADEC) can result in a loss of engine performance, including an in-flight shut down of an aircraft engine. Malfunctions in other critical electronic systems, such as flight control systems or a general avionics unit, can result in difficulty controlling or navigating the aircraft.
Aircraft with short flight times, such as small commercial aircraft, accumulate high numbers of thermal cycles per flight hour as they move between generally warmer ambient temperatures near the ground and generally colder ambient temperatures at flight altitude. Such thermal cycling degrades electronic systems, especially on-engine EECs and FADECs, and non-avionics bay electronics, due to failures of solder joints and electronic component attachment leads from Low Cycle Fatigue (LCF) damage. In addition, powering up and powering down electronic systems contributes to the thermal stresses experienced by the electronic components. Vibration effects also contribute to failures of solder joints and attachment leads. Electronic system designs, particularly for commercial engine controls, are demanding ever-increasing service life requirements. Service life requirements as high as 100,000 flight hours are not uncommon. The service life requirements can limit the selection of components available to perform the necessary control functions, which leads to larger, heavier, and more expensive designs than what could be achieved with current state of the art packages. This is especially true when a specified environment for the service life requirement represents a worst-case environment that is beyond the conditions experienced by the majority of the engine controls.
Health monitoring systems have been described that permit the use of Commercial Off The Shelf (COTS) electrical components. A health monitoring system indicates when a monitored electronic system has experienced enough degradation that it should be serviced or replaced. The ability to reliably identify failing electronic systems well ahead of the point of failure permits the use of COTS electrical components. Some of the health monitoring systems known in the art sense and record the conditions experienced by the electronics systems, e.g. vibration, temperature cycles, etc., and employ algorithms to indicate when the useful life of the electronics is near. Such systems rely on the ability of the sensed conditions to represent all or most of the environmental stresses experienced by the electronic systems. Other health monitoring systems measure portions of a circuit performing a desired system function, where the circuit can still perform its function after some measurable degradation of the circuit. Such systems are limited to designs where the circuit has a built-in reserve capacity to perform its function. In addition, the warning lead time is limited because of the use of identical components in the circuit. Once one component fails, the identical remaining components, essential for the circuit to function, are likely to fail soon after.